A) Field of the Invention
The present invention relates to an antenna array, and more particularly to an antenna array which uses a simplified beam forming network.
B) Description of Related Art
FIG. 1 shows a conventional antenna array 10. The antenna array 10 includes an antenna component 20 and a beam forming network 30. The antenna component 20 includes five individual antenna elements 21-25, whereas, the beam forming network 30 includes a complex set of hardware to receive, process and route a sum beam pattern 31 and a difference beam pattern 33 to the antenna component 20.
The conventional antenna array 10, as shown in FIG. 2, is capable of radiating the sum and difference beam patterns 31 and 33 to nine beam locations designated as A through I. The sum and difference beam patterns 31 and 33 are produced at the nine different locations by exciting different combinations of antenna elements 21-25. In particular, the antenna array 10 produces sum and difference beam patterns 31 and 33 at locations A through C when antenna elements 21 through 23 are excited, at beam locations D through F when antenna elements 21 through 25 are excited, and at beam locations G through I when antenna elements 23 through 25 are excited.
The antenna elements 21-23 have a V-shaped configuration. As is known in the art, this configuration is provided to reduce the undesirable effects of a phenomenon referred to as beam-coning.
FIG. 3, shows an example of the sum beam pattern 31 and difference beam pattern 33 which are received and processed by the conventional antenna array 10. These beam patterns interrogate each of the nine beam locations to identify aircrafts or other devices which are operating in a region of interest. The use of sum and difference beam patterns such as these to identify and communicate with the aircrafts is well known in the art and is described, for example, in U.S. Pat. No. 4,316,192. This document is hereby incorporated by reference as if set forth fully herein.
The beam forming network 30 of the conventional antenna array 10 is responsible for producing the sum and difference beams patterns 31 and 33 at each of the nine locations A through I. To perform this function, the beam forming network 30 includes a plurality of devices. Specifically, the beam forming network 30 includes four single pole double throw (SP2T) switches 33, eight fixed line length phase shifters 34, four 180.degree. hybrid RF devices 35, five couplers 36, and three single pole triple throw (SP3T) switches 37. A description of how the beam forming network 30 produces the sum and difference patterns at one or more of the nine beam locations is presented below.
The processing begins when the sum beam pattern 31 enters the beam forming network 30 through SP3T 37A, and the difference beam pattern 33 enters through SP3T 37B.
The sum beam pattern 31 is then routed to the coupler 36A. The coupler 36A splits the sum beam pattern 31 such that one component is sent directly to SP2T switch 33B and the other component is sent to the 180.degree. hybrid RF device 35A. The 180.degree. hybrid RF device 35A further splits the sum beam pattern into two components. The first component is sent through phase shifter 34A to SP2T switch 33A, and, the second component is sent through phase shifter 34B to SP3T switch 37C.
The difference beam pattern 33 is routed directly to the 180.degree. hybrid RF device 35A. This device similarly splits the difference beam pattern 33 into two components. The first component is sent through phase shifter 34A to SP2T switch 33A, and, the second component is sent through phase shifter 34B to SP3T switch 37C.
The sum and difference beam patterns 31 and 33 received at SP2T switches 33A-B and SP3T switch 37C are then routed to antenna elements 21-23 and propagated into space. When these three antenna elements are excited, as indicated above, the sum and difference beam patterns 31 and 33 will be produced at one of the locations A through C.
The exact location of the beam patterns will depend of the settings of the phase shifters 34A-B which adjust the phase of an incoming signal by increments of 45.degree.. For example, the sum and difference beam patterns 31 and 33 will be produced at location A if the phase shifters 34A-B are positioned at a first setting. Similarly, the sum and difference beam patterns 31 and 33 will be produced at location B if the phase shifters 34A-B are positioned at a second setting, and at location C when if the phase shifters 34A-B are positioned at a third setting.
The antenna array 10 shown in FIG. 1 will similarly produce the sum beam pattern 31 and difference beam pattern 33 at the remaining locations D through I depending on the configuration of the of the SP2T switches 33, the phase shifters 34, and the SP3T switches 37. The process for producing sum and difference beam patterns 31 and 33 at these remaining locations is similar to that described above for locations A-C.
The conventional antenna array 10 described above and shown in FIG. 1 does, however, have certain drawbacks. Most notably, the antenna array 10 has a poor performance reliability and a high cost. These undesirable factors are attributable to the fact that the beam forming network 30 of the antenna array 10 uses a large number of components.
In view of these drawbacks, there currently exists a need for an antenna array which has a strong performance reliability and low cost where the beam forming network used by the antenna array has a simplified configuration and uses a small number of components.